Hi
setting the timeing sounds like a 5 second job.
always takes me absolutely yonks.
how the f£$%$ do you keep the magneto still while you tighten the pinion???
I set everything up, then tap the pinion on
then when i tighten it everything moves out of position
its infuriating.
and the same with the tappet clearances. i make the gap .003 then tighten it up and the gap is then totally different
aaaaarrrggghhh 
When you are setting the tappets partially tighten the tappet adjuster lock nut...You need to tighten it enough so that you can still move both the tappet head and the locknut by turning only the locknut.
So, first set the gap slightly wide, partially tighten the locknut and then turn the locknut and the tappet head together to set the correct gap. Finally just nip up the locknut...
Partially tightening it will stop things moving around.
Make sure you follow the correct procedure for setting the tappets...this is critical due to the design of the BSA cam profile.
Turn the engine over until the inlet valve has just closed (ie the tappet is just free to rotate). Then set the exhaust clearance. Then turn the engine over until the exhaust tappet has just taken up the clearance (ie just as the tappet will no longer rotate)...Then set the inlet tappet.
If your engine is 'pinking'..Which is what that rattly noise is...The ignition may be too far advanced and you will damage it by running continuously in that condition.
So you will have to check the timing to determine that it is set at 3/8"BTDC with the adv/rtd lever set in the fully advanced position...
I know you have quite a high compression piston fitted as well...This may also cause pinking (pre ignition) if you let the engine 'slog' under load. Tuned ones need to be revved more to avoid this....
Lap the magneto drive gear to the armature taper with some fine grinding paste to ensure you have a good fit of the gear to the taper.
Also check that the back of the drive gear is not contacting the front of the mag when fitted. This will obviously prevent the taper engaging correctly. Finally, examine the gear closely for cracks...They do occasionally fail and that prevents the taper functioning correctly as a 'lock' when the gear is fitted.
Fit a spring washer under the mag drive gear nut...that can help as well.
When all that is attended to reset the engine and mag and carefully fit the gear. Give it a sharp tap with a hammer and a piece of tube/ socket on the face of the gear, taking care not to damage the magneto armature thread. Refit the washer and nut and tighten...
You may still find it will take more than one go to get it right but you just have to keep at it...You can also wedge the intermediate gear and mag gear teeth to help stop things moving...I use a phosphor bronze wedge I made for the purpose...many use a screwdriver. When tightening the nut do it slowly and progressively..If everything is in good order it is very unusual for the tming to 'slip' once set.....Ian
email (option): ian@wright52.plus.com
Hi Panic...I was referring to the tappet setting query that Maxwell made...
BSA cams of this period have 'silencing ramps' ground into the profile. This means they have a very long but gradual initial opening and final closing period.
Consequently, the tappet clearance is at its maximum for only a very short amount of the cams movement.
Therefore, each cam must be correctly positioned before adjustments are made to ensure the clearance set is a 'true' setting..This particularly applies to B Series iron engines which only have a .003" clearance and therefore a smaller margin for error. However, M Series cams and the ones fitted to B Series alloy engines also have the same feature, so the same procedure should be applied to achieve an accurate result....Ian
email (option): ian@wright52.plus.com